1. Technical Field
The present invention relates to a positioning device for carrying out positioning on the basis of signals from positioning satellites, a control method for the positioning device, a control program for the positioning device, and a computer-readable recording medium in which the control program for the positioning device is recorded.
2. Related Art
There has been practically used a positioning system for detecting the present position of a GPS receiver by using a satellite navigation system such as GPS (Global Positioning System) or the like.
The GPS receiver receives signal electric waves from three or more GPS satellites (hereinafter referred to satellite signals), for example, and calculates the distance between each GPS satellite and the GPS receiver (hereinafter referred to as pseudo range) on the basis of the difference between the transmission time of the satellite signal from each GPS satellite and the reception time of the satellite signal concerned at the GPS receiver (hereinafter referred to as delay time). Then, the GPS receiver carries out the positioning calculation of the present position of the GPS receiver by using information on the position on the satellite orbit and pseudo range of each GPS satellite.
Here, in some cases, the GPS receiver receives indirect waves induced when the electric wave from the GPS satellite is reflected from buildings, etc. (hereinafter referred to as a multipath). The multipath thus induced reaches the GPS receiver with a delay time with respect to the direct wave from the GPS satellite because it is induced due to the reflection of the electric wave from the GPS satellite from the buildings, etc. As a result, there is a problem that the pseudo range is deviated to be longer, and a large error occurs in the positioning calculation.
On the other hand, there has been proposed a technique of carrying out positioning while excluding the multipath by taking it into consideration that the signal intensity of the multipath is weaker than the direct wave (for example, JP-A-2001-272450 (FIG. 2, etc.)).
However, in an urban area where tall buildings stand side by side, there are some cases where it is impossible to receive direct waves from GPS satellites whose number is needed for the positioning, and there is a problem that if the multipath is excluded, the positioning itself would be impossible.